Quote from Wikipedia X11 color names:
In computing, on the X Window System, X11 color names are represented in a simple text file, which maps certain strings to RGB color values. It is shipped with every X11 installation, hence the name, and is usually located in ‹X11root›/lib/X11/rgb.txt.
It is not known who originally compiled the list. The list shows a continuity neither in selected color values nor in color names, and many color triplets have multiple names. Despite this, graphic designers and others got used to them, making it practically impossible to introduce a more stringent and logical alias list.
Why it's like that? Because it's the unix philosophy!
Time to reread: The X-Windows Disaster.